In the June 2010 AQA 6X paper, Section 2 Task B, the question asks you to sketch how you positioned your fiducial mark to investigate the time period for an oscillating chain of paper clips. It then asks you to explain why.
The first mark point was obviously for placing it at the equilibrium position, but the second mark given in the mark scheme was that the fiducial mark should be placed 'below some 3/4 of the length of the chain, and ideally positioned below the end of the chain'.
In the examiners report, they commented that 'a worrying number of students positioned the fiducial mark behind the chain instead of below, and that relatively few could explain why the fiducial mark should be positioned like so'. My physics teacher does not understand why it should be ideally beneath the chain, or why it is not acceptable to place it behind. Can anyone explain the reasons behind this?

(Original post by tigerboobs)
In the June 2010 AQA 6X paper, Section 2 Task B, the question asks you to sketch how you positioned your fiducial mark to investigate the time period for an oscillating chain of paper clips. It then asks you to explain why.
The first mark point was obviously for placing it at the equilibrium position, but the second mark given in the mark scheme was that the fiducial mark should be placed 'below some 3/4 of the length of the chain, and ideally positioned below the end of the chain'.
In the examiners report, they commented that 'a worrying number of students positioned the fiducial mark behind the chain instead of below, and that relatively few could explain why the fiducial mark should be positioned like so'. My physics teacher does not understand why it should be ideally beneath the chain, or why it is not acceptable to place it behind. Can anyone explain the reasons behind this?

Increased risk of parallax errors if the mark and the pendulum are at different distances from your eyeball imo.

tbh it's something you could work around if you thought about it, though you should explain so the examiner doesn't think you're unaware of the possibility.